Defects in articular cartilage associated with trauma and osteochondritis dissecans are difficult for surgeons to repair. The patient can expect to face progressive deterioration over time leading to advanced osteochondritis, arthritis and the possibility of joint replacement. The knee as a weight-bearing joint is particularly susceptible to this problem, although similar injuries to the articular cartilage of other joints in humans and other mammals also occur with regularity.
FIG. 1 illustrates a knee joint 10 between the distal end 11 (i.e., that surface farthest from the center of the body) of a femur 12 and the proximal end 13 (i.e., that surface closest to the center of the body) of the tibia 14. Portions 15, 17 of the connective tissue which movably ties the femur 12 to the underlying tibia 14 and fibula 18 are shown. Normally interposed between opposing surfaces of the femur 12 and tibia 14 are lateral and medial meniscus cartilages, 21 and 23, respectively. The condyles 22 at the distal end 11 of the femur 12 are normally supported by the meniscus cartilages 21 and 23 on the proximal end 13 of the tibia 14. Normally, the distal end 11 of femur 12, including the condyles 22 is covered by a layer 28 of cartilaginous material about 5 mm thick, referred to as the articular cartilage. Articular cartilage 28 forms a generally resilient pad which is fixed on the distal surface 11 of the femur 12 to protect the femur from wear and mechanical shock. The articular cartilage 28, when lubricated by fluid in the knee joint 10, provides a surface which is readily slidable on the underlying surfaces of the meniscus cartilages 21 and 23 or on the proximal surface 13 of the tibia 14 if one or both of the meniscus cartilages 21, 23 should be partially or totally absent. Nevertheless, the articular cartilage 28 may become damaged in that it may be torn 24 or holed or become excessively worn.
Methods have been used to repair such articular cartilage damage before it can spread or result in eventual injury or wear to the underlying condyles 22, meniscus cartilages 21, 23, or tissues associated with the tibia 14. It has been known to replace damaged articular cartilage with a layer of fibrous material. See U.S. Pat. No. 5,067,964, incorporated herein by reference. Repairing defects in articular cartilage in human or other mammalian joints therefore requires materials that have been approved by the FDA for use in the human body. It is often problematic to find such materials that are commercially available and relatively low in cost in which completion of the repairs are within the skills of qualified orthopedic surgeons. Another repair method involves packing an articular cartilage defect with bits of cancellous and cortical bone (Soviet Patent SU 1454423, Jun. 27, 1986, incorporated herein by reference) that have been chipped from defect-free bone. This latter technique avoids using foreign materials but, like the former methods, does not preserve the original orientation of bone and cartilage.
Prostheses have also been used for replacement of the joint itself. Problems encountered after implanting such prostheses are usually caused by the cements used to attach the prostheses to the host bone. Further, some prostheses associated with joint replacements are actually much larger than the degenerated tissue that needs to be replaced so that extensive portions of healthy bone are typically removed to accommodate the prostheses.
A vastly improved method and apparatus for cartilage repair is disclosed in a copending and commonly owned patent application entitled "Apparatus and Methods for Articular Cartilage Defect Repair", filed Mar. 7, 1995 and assigned U.S. application Ser. No. 08/399,428, the entire contents of which are incorporated herein by reference. U.S. application Ser. No. 08/399,428 discloses an apparatus and method for drilling out damaged cartilage and replacing the damaged portion with healthy cartilage from another part of the body. A section of the damaged cartilage and the bone thereunder is drilled-out. A bone plug, with healthy cartilage attached to its surface, is cut from another section of bone and then inserted into the drilled-out section of the damaged cartilage. The new bone plug with healthy cartilage provides a solution to the cartilage repair problem.
While the method and apparatus for cartilage repair disclosed in U.S. application Ser. No. 08/399,428 is an improvement over the prior art, a difficulty remains in that the healthy cartilage attached to the bone plug should be in registration with the remaining cartilage in the damaged cartilage area. In other words, the new healthy cartilage should be at the same level as the surrounding cartilage. To accomplish this, the drilled-out portion should be drilled at the same angle and size as the healthy bone plug. Otherwise, for example, if the healthy bone plug is cut at an angle, when it is inserted into a damaged area where the drilled-out portion is normal to the bone surface the healthy cartilage will not properly register with the surrounding cartilage and the repair may be unsuccessful or of limited success. During many bone cutting operations, the surgeon cannot directly see the surface of the bone to ensure that a bone cutter is correctly orientated with respect to the bone surface. Thus, the need remains to develop an apparatus and method which cuts bone at a repeatable orientation with respect to the bone surface.